[Coronary blood flow during stochastic stimulation of the canine heart]. / Koronarnyi krovotok pri stokhasticheskoi stimuliatsii serdtsa sobaki.

Changes of mechanical activity and coronary blood flow induced by haphazard uncorrelated sequence of stimuli, were studied in the dog heart. The total coronary blood flow did not differ from one during determined regimen of the same mean frequency. Whereas relative contribution of systolic coronary flow increased and that of diastolic one decreased. The analysis of phasic blood flow in coronary vessels during potentiated and extrasystolic contractions, was performed.

[Ca2+ participation in vasodilator reactions]. / Uchastie Ca2+ v sosudorasshiritel'nykh reaktsiiakh.

Stimulation of alpha-adrenoceptors was simulated by intraarterial injection of 0.6 mmol CaCl2 in acute experiments on resting muscles of the dog hind leg. It has been demonstrated that alpha-adrenergic stimulation of metabolism in skeletal muscles has a vasodilative effect in the muscle-supplying vessels. It has been also shown that imitation of alpha-adrenergic stimulation effect by intraarterial injection of CaCl2 causes Ca- and alpha-adrenergic-dependent vasodilative reactions. It is suggested that disturbance of vasodilative effects caused by alpha-adrenergic stimulation in the effector tissues, counteracting the direct constrictive alpha-adrenoceptor effect in the smooth muscle cells of the vessel wall, can lead to systemic impairment of the vascular tone.

[Effect of sympathetic nerve stimulation on myocardial reactive hyperemia]. / Vliianie razdrazheniia simpaticheskikh nervov na reaktivnuiu giperemiiu miokarda.

It has been established in experiments on 25 dogs that the peak of reactive hyperemia (RH) of the myocardium cannot be regarded as an absolute criterion of the coronary dilatory reserves. Stimulation of the stellate ganglion under the conditions of arterial blood pressure stabilization increased the peak of RH. After-effect of the sympathetic nerve stimulation also led to a rise in the peak of RH as compared with control.

Certain characteristics of myocardial contractility of isovolumic dog heart at randomly variable heart rhythm.

The relationship "heart rate - left ventricular pressure" was investigated in the isolated canine heart perfused with constant pressure at different preloads. Rhythmical stimulation was performed with constant stimulus interval duration and with stimulus intervals randomly changed near the average value (150-200 stimuli in series). Correlation and dispersion function analysis show that rhythm dispersion had a negative inotropic effect which was independent of the preload of the ventricle in the range of 120-180 beat/min, but this dependence occurred with low rats of stimulation. This method is proposed for the assessment of contractility under conditions of heart rate variations (physiological and pathological arrhythmias).

[Pharmacological analysis of a disorder in the mechanisms of coronary vessel reactivity in an experimental model of coronary insufficiency]. / Farmakologicheskii analiz narusheniia mekhanizmov reaktivnosti koronarnykh sosudov na éksperimental'noi modeli koronarnoii nedostatochnosti.

In stimulation of the heart work with inadequate perfusion, the reactivity of coronary vessels is often disturbed which is revealed by the enhancement of extravascular contraction or by the absence of an adequate vasodilatation. The analysis of disturbance mechanisms in the reactivity of coronary vessels has been carried out with the aid of two groups of pharmacologic substances, one exercising a dilatating effect on the coronary vessels and the other affecting the calcium metabolism. One group included adenosine and verapamil (as antagonists of the action of calcium) as well as etmozine-blocker of the sodium channels capable of affecting the level of Ca+2 through Na-Ca metabolism; the other group included caffeine, calcium chloride, norepinephrine. The results suggest that adaptive reactions of the coronary vessels are closely connected with the calcium metabolism in smooth muscles of the vascular wall. Hence, while using vasodilators to treat coronary insufficiency, the approach to a selection of drugs with different effects on electro-mechanical conjunction in smooth muscles of vascular wall should be differentiated.

[Analysis of depression of contractions of the isolated dog heart following paired stimulation]. / Analiz depressii sokrashchenii izolirovannogo serdtsa sobaki posle parnoi stimuliatsii

In 30 experiments in isolated canine hearts perfused with whole donor blood disorders in myocardial contractions were studied following the termination of paired stimulation. It was concluded that the cause of depression of cardiac contractions following paired stimulation is not myocardial hypoxia and energy reserve exhaustion during enhanced mechanical activity of the heart, but a dissociation of the electric and mechanical processes in the myocardium; switching off the second (stand-by) action potential together with the termination of the paired stimulation caused disorders in the regimen of coupling processes that have established themselves under this form of electric stimulation. This suggestion is supported by the fact that repeated paired stimulation during depression is capable of producing the same stimulating effect upon the cardiac contractions as the initial one. The depression was eliminated by the administration of potassium ions and catecholamines.

[Changes in the glycogen content of the dog myocardium at various phases of the cardiac cycle with a normal coronary blood flow]. / Izmeneniia soderzhaniia glikogena v miokarde sobaki v raznye fazy serdechnogo tsikla pri normal'nom koronarom krovotoke

Alterations in content of glycogen in myocardium of isolated heart of dog were studied at different phases of heart cycle by means of a special apparatus for myocardial biopsy and prompt freezing. Significant alterations in content of glycogen were observed during heart contraction. The maximal decrease (by 30.7%) in content of glycogen was found in preparations, obtained immediately after the R peak of electrocardiogramm. During the later steps of refractory period an increase in content of glycogen was observed and at the point, positioned 0.25 sec apart from the R peak, content of glycogen exceeded by 91.7% the initial level.

[Characteristics of reaction of the coronary vessels and metabolism of the myocardium in changing over from high to low frequency electric stimulation of the heart]. / Osobennosti reaktsii venechnykh sosudov i metabolizma miokarda pri perekhode ot vysokikh chastot elektrostimuliatsii serdtsa k nizkim

In 22 tests on an isolated dog's heart perfused from a donor the oxygen intake, coronary blood flow, oxyhemoglobin content in the coronary venous blood and arterio-venous difference were compared with a jumpwise and gradual depression of the electrostimulation of the heart rhythm from 4.5 down to 2.0-2.5 Hd. With an abrupt reduction of the contraction rhythm in the myocardium these persisted hypermetabolism outwardly resembling an acquintance of the oxygen debt, although the preceding work of the heart proceeded without any signs of hypoxia. There could be noted an elevated consumption of oxygen, an increased coronary circulation, a diminished utilization of lactic acid and even its ejection. Worthy of note is the fact that an elevated oxygen intake was ensured at the expense of the larger coronary circulation with a reduced extraction of oxygen, so that the saturation of the coronary venous blood with oxygen exceeded the initial values. With a gradual slowing down of the rhythm there were no manifestation of hypermetabolism: the consumption of oxygen returned back to its initial level, the coronary circulation decreased, while extraction of oxygen was rising. The data obtained are considered in the light of the metabolic hypothesis on the regulation of the vascular tone.